Degradation of sulphachloropyridazine sodium in column reactor packed with CoFe2O4 - loaded quartz sand via peroxymonosulfate activation: Insights into the amorphous phase, efficiency, and mechanism

A simple, low-cost, and highly efficient process is required to produce free radicals from peroxides for degradation of organic pollutants. In this study, for the first time, CoFe2O4 was immobilized on quartz sand support (CoFe2O4-QS) and then packed into the continuous flow column reactor to activate peroxymonosulfate (PMS) for degradation of sulphachloropyridazine sodium (SCP) in water. CoFe2O4 was synthesized at low temperature (300 degrees C, CoFe2O4-QS-300) and exhibited an amorphous structure to facilitate more efficient electron transfer. The continuous flow column reactor worked efficiently at adjustable flow rates and within a wide pH range. Our results showed that over 90% of SCP with an initial concentration of 20 mg L-1 was degraded under the conditions of 10 g CoFe2O4-QS-300 (1.0% CoFe2O4 loading), 75 mg L-1 PMS and a retention time of 46.1 s. In comparison with batch reactor, the continuous flow reactor simplified the process of catalyst reuse and significantly reduced the amount of metal leaching, in addition to the similar performance for SCP removal. Both the sulfate and hydroxyl radicals were produced during PMS activation. Meanwhile, the synergistic catalytic effects between solid Co(II) and Fe(III) were investigated and the associated mechanism was proposed, i.e. the presence of Fe(III) guaranteed the formation of hydroxyl groups, and then the nearby Co(II) accepted the hydroxyl groups to form Co(II)-OH complexes, which played a critical role in the activation of PMS. Moreover, the intermediates of SCP degradation were identified and the possible degradation pathways were proposed. Taken all together, the continuous flow column reactor developed in this study represents an efficient, novel and cost effective method for the removal of organic contaminants in industrial wastewater.